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>Chapter 19. Here Documents</TD
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><H1
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><A
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></A
>19.1. Here Strings</H1
><P
><A
NAME="HERESTRINGSREF"
></A
></P
><A
NAME="AEN17841"
></A
><BLOCKQUOTE
CLASS="BLOCKQUOTE"
><P
CLASS="LITERALLAYOUT"
>A&nbsp;<I
CLASS="FIRSTTERM"
>here string</I
>&nbsp;can&nbsp;be&nbsp;considered&nbsp;as&nbsp;a&nbsp;stripped-down&nbsp;form&nbsp;of&nbsp;a&nbsp;<I
CLASS="FIRSTTERM"
>here document</I
>.<br>
It&nbsp;consists&nbsp;of&nbsp;nothing&nbsp;more&nbsp;than&nbsp;<B
CLASS="COMMAND"
>COMMAND &#60;&#60;&#60; $WORD</B
>,<br>
where&nbsp;<TT
CLASS="VARNAME"
>$WORD</TT
>&nbsp;is&nbsp;expanded&nbsp;and&nbsp;fed&nbsp;to&nbsp;the&nbsp;<TT
CLASS="FILENAME"
>stdin</TT
>&nbsp;of&nbsp;<B
CLASS="COMMAND"
>COMMAND</B
>.<br>
	&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</P
></BLOCKQUOTE
><P
>As a simple example, consider this alternative to the <A
HREF="internal.html#ECHOGREPREF"
>echo-grep</A
> construction.</P
><P
>	  <TABLE
BORDER="0"
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><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
># Instead of:
if echo "$VAR" | grep -q txt   # if [[ $VAR = *txt* ]]
# etc.

# Try:
if grep -q "txt" &#60;&#60;&#60; "$VAR"
then   #         ^^^
   echo "$VAR contains the substring sequence \"txt\""
fi
# Thank you, Sebastian Kaminski, for the suggestion.</PRE
></FONT
></TD
></TR
></TABLE
>
        </P
><P
><A
NAME="HSREAD"
></A
></P
><P
>Or, in combination with <A
HREF="internal.html#READREF"
>read</A
>:</P
><P
>	<TABLE
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CLASS="PROGRAMLISTING"
>String="This is a string of words."

read -r -a Words &#60;&#60;&#60; "$String"
#  The -a option to "read"
#+ assigns the resulting values to successive members of an array.

echo "First word in String is:    ${Words[0]}"   # This
echo "Second word in String is:   ${Words[1]}"   # is
echo "Third word in String is:    ${Words[2]}"   # a
echo "Fourth word in String is:   ${Words[3]}"   # string
echo "Fifth word in String is:    ${Words[4]}"   # of
echo "Sixth word in String is:    ${Words[5]}"   # words.
echo "Seventh word in String is:  ${Words[6]}"   # (null)
                                                 # Past end of $String.

# Thank you, Francisco Lobo, for the suggestion.</PRE
></FONT
></TD
></TR
></TABLE
>
        </P
><P
><A
NAME="HSLOOP"
></A
>It is, of course, possible to feed
	  the output of a <I
CLASS="FIRSTTERM"
>here string</I
>
	  into the <TT
CLASS="FILENAME"
>stdin</TT
> of a <A
HREF="loops.html#LOOPREF00"
>loop</A
>.</P
><P
><TABLE
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><FONT
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><PRE
CLASS="PROGRAMLISTING"
># As Seamus points out . . .

ArrayVar=( element0 element1 element2 {A..D} )

while read element ; do
  echo "$element" 1&#62;&#38;2
done &#60;&#60;&#60; $(echo ${ArrayVar[*]})

# element0 element1 element2 A B C D</PRE
></FONT
></TD
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></P
><P
><A
NAME="HSPRE"
></A
></P
><DIV
CLASS="EXAMPLE"
><A
NAME="PREPENDEX"
></A
><P
><B
>Example 19-13. Prepending a line to a file</B
></P
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><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# prepend.sh: Add text at beginning of file.
#
#  Example contributed by Kenny Stauffer,
#+ and slightly modified by document author.


E_NOSUCHFILE=85

read -p "File: " file   # -p arg to 'read' displays prompt.
if [ ! -e "$file" ]
then   # Bail out if no such file.
  echo "File $file not found."
  exit $E_NOSUCHFILE
fi

read -p "Title: " title
cat - $file &#60;&#60;&#60;$title &#62; $file.new

echo "Modified file is $file.new"

exit  # Ends script execution.

  from 'man bash':
  Here Strings
  	A variant of here documents, the format is:
  
  		&#60;&#60;&#60;word
  
  	The word is expanded and supplied to the command on its standard input.


  Of course, the following also works:
   sed -e '1i\
   Title: ' $file</PRE
></FONT
></TD
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></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="MAILBOXGREP"
></A
><P
><B
>Example 19-14. Parsing a mailbox</B
></P
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><FONT
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><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
#  Script by Francisco Lobo,
#+ and slightly modified and commented by ABS Guide author.
#  Used in ABS Guide with permission. (Thank you!)

# This script will not run under Bash versions -lt 3.0.


E_MISSING_ARG=87
if [ -z "$1" ]
then
  echo "Usage: $0 mailbox-file"
  exit $E_MISSING_ARG
fi

mbox_grep()  # Parse mailbox file.
{
    declare -i body=0 match=0
    declare -a date sender
    declare mail header value


    while IFS= read -r mail
#         ^^^^                 Reset $IFS.
#  Otherwise "read" will strip leading &#38; trailing space from its input.

   do
       if [[ $mail =~ ^From  ]]   # Match "From" field in message.
       then
          (( body  = 0 ))           # "Zero out" variables.
          (( match = 0 ))
          unset date

       elif (( body ))
       then
            (( match ))
            #  echo "$mail"
            #  Uncomment above line if you want entire body
            #+ of message to display.

   elif [[ $mail ]]; then
      IFS=: read -r header value &#60;&#60;&#60; "$mail"
      #                          ^^^  "here string"

      case "$header" in
      [Ff][Rr][Oo][Mm] ) [[ $value =~ "$2" ]] &#38;&#38; (( match++ )) ;;
      # Match "From" line.
      [Dd][Aa][Tt][Ee] ) read -r -a date &#60;&#60;&#60; "$value" ;;
      #                                  ^^^
      # Match "Date" line.
      [Rr][Ee][Cc][Ee][Ii][Vv][Ee][Dd] ) read -r -a sender &#60;&#60;&#60; "$value" ;;
      #                                                    ^^^
      # Match IP Address (may be spoofed).
      esac

       else
          (( body++ ))
          (( match  )) &#38;&#38;
          echo "MESSAGE ${date:+of: ${date[*]} }"
       #    Entire $date array             ^
          echo "IP address of sender: ${sender[1]}"
       #    Second field of "Received" line    ^

       fi


    done &#60; "$1" # Redirect stdout of file into loop.
}


mbox_grep "$1"  # Send mailbox file to function.

exit $?

# Exercises:
# ---------
# 1) Break the single function, above, into multiple functions,
#+   for the sake of readability.
# 2) Add additional parsing to the script, checking for various keywords.



$ mailbox_grep.sh scam_mail
  MESSAGE of Thu, 5 Jan 2006 08:00:56 -0500 (EST) 
  IP address of sender: 196.3.62.4</PRE
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><P
>Exercise: Find other uses for <I
CLASS="FIRSTTERM"
>here
           strings</I
>, such as, for example, <A
HREF="mathc.html#GOLDENRATIO"
>feeding input to
           <I
CLASS="FIRSTTERM"
>dc</I
></A
>.</P
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